JP4124680B2

JP4124680B2 - Magnetic recording medium manufacturing method and manufacturing apparatus thereof

Info

Publication number: JP4124680B2
Application number: JP2003068816A
Authority: JP
Inventors: 喜代司高橋; 淳一今村; 知房今井
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 2002-03-15
Filing date: 2003-03-13
Publication date: 2008-07-23
Anticipated expiration: 2023-03-13
Also published as: JP2003338021A

Description

【０００１】
【発明の属する技術分野】
本発明は、絶縁性基材に備えた強磁性金属薄膜の表面に硬質炭素膜を形成した磁気記録媒体とその製造方法及びその製造装置に関する。
【０００２】
【従来の技術】
最近情報記録分野では磁気記録分野での高記録密度化に伴い、記録膜のみならず、記録膜を保護する保護膜の性能が製品の信頼性を決定する重要な基本技術の一つである。また、安価に磁気記録媒体を提供するためには、記録膜及び保護膜の高速成膜も必須である。記録膜の高速成膜技術は真空蒸着法の進歩に伴い確立されているが、保護膜は記録膜全面に渡り欠陥個所無く覆うことが要請されるため緻密な成膜方法が要請され、スパッタ法又はプラズマＣＶＤ（化学蒸着）法が検討されている。
【０００３】
上記保護膜の成膜方法としては、成膜レートの高いプラズマＣＶＤ法が高速成膜では有利であり、各種の提案がされている。プラズマＣＶＤ法で成膜した膜質を向上させ信頼性を確保するために、高エネルギーでの成膜が必須となる。しかしながら高エネルギーでの成膜では、高電流を必要とするため、記録膜へ電流を供給する抵抗ローラ自体の通電点を増やす必要がある。
【０００４】
一般的に用いられる金属ローラでは、接触点の抵抗値が極めて低いため、一点当りの電流値が高くなり、当該接触点における接触抵抗及び／又は記録膜の抵抗値に起因するジュール熱が発生し、当該ジュール熱で絶縁性基材及び／又は記録膜の損傷や保護膜自体の欠陥が発生し、これら欠陥が要因となって記録膜への記録再生欠陥が増加する。さらに、前記の欠陥を有する媒体を高温高湿環境に放置した場合、これらの何れかの欠陥を核とする錆が記録膜に発生し、記録又は再生が不能となる等の信頼性を著しく低下させるという課題が発生する。この課題に対して、保護膜を成膜する際に記録膜に適正化した表面抵抗値を有する抵抗ローラを介して電流を供給する技術が提案され、一般的用途に適応する磁気記録媒体の信頼性については解決されている。
【０００５】
しかし、過酷な使用条件、例えばヘリカルスキャン型で高速回転の小径シリンダーを搭載したビデオテープレコーダにおいては、微少欠陥に起因するドロップアウトあるいはエラーレートが増加するという問題があった。また、高温高湿環境下保存後においては、記録膜への密着強度および保護膜の膜質の低下により、ドロップアウトが大幅に増加するという問題があった。ヘリカルスキャン型の小径シリンダーを搭載したビデオテープレコーダの例としては、下記特許文献１が提案されている。
【０００６】
【特許文献１】
特開平４−２３６５８８号公報
【０００７】
【発明が解決しようとする課題】
本発明は、前記従来の問題を解決するため、より過酷な用途に対しても高信頼性を維持できる磁気記録媒体とその製造方法及びその製造装置を提供することを目的とする。
【０００８】
【課題を解決するための手段】
前記目的を達成するため、本発明の磁気記録媒体の製造方法は、電気的絶縁性フィルムの表面に、強磁性金属薄膜と硬質炭素膜と、潤滑剤層をこの順番で含み、裏面にバックコート層を含む磁気記録媒体の製造方法であって、導電性軸とその周囲の厚み方向に電気的抵抗値傾斜を有し、電気的抵抗値が低い面を最内層側とし電気的抵抗値が高い面を最外層側とした抵抗ローラの最外層と、前記強磁性金属薄膜とを接触させ、前記抵抗ローラの前記導電性軸に電圧を印加しつつ減圧槽に炭化水素反応ガスを供給してプラズマＣＶＤにより、前記強磁性金属薄膜の表面に硬質炭素膜を形成することを特徴とする。
【００１０】
次に本発明の磁気記録媒体の製造装置は、抵抗ローラを備えた減圧槽に、炭化水素反応ガスを供給してプラズマＣＶＤにより、絶縁性フィルムの表面に形成されている強磁性金属薄膜の表面に硬質炭素膜を形成し、磁気記録媒体を製造する装置であって、前記抵抗ローラは、厚み方向に電気的抵抗値が傾斜しており、電気的抵抗値の低い面を最内層側とし電気的抵抗値の高い面を最外層側とし、前記抵抗ローラの軸に電圧を印加するための導電性軸を備えたことを特徴とする。
【００１１】
【発明の実施の形態】
本発明において、ドロップアウト数値が２００個以下であることは、記録再生欠陥が少ないことを意味する。また、スチル寿命が１０分以上であることは、耐食性が高いことを意味する。したがって、本発明の磁気記録媒体は、記録再生欠陥が少なく、かつ耐食性が高い特性を有する。
【００１２】
本発明において、硬質炭素膜は、強磁性金属薄膜の表面に厚さ５ｎｍ以上３０ｎｍ以下が好ましく、さらに８〜１５ｎｍの厚みで形成されていることが好ましい。前記の範囲であれば、緻密で均一な記録が可能となる。ここで、硬質炭素膜とは、アモルファスカーボンのことであり、別名ダイヤモンド状炭素膜ともいう。
【００１３】
また、強磁性金属薄膜は、酸化Ｃｏを含む強磁性金属を斜方蒸着により酸素を導入しながら形成することが好ましい。強磁性金属薄膜の別の例は、Ｃｏ−Ｎｉ−Ｏ，Ｃｏ−Ｎｉ−Ｃｒ，Ｃｏ−Ｃｒなどである。強磁性金属薄膜の厚みは、０．０５〜０．３μｍの範囲が好ましい。斜方蒸着は当業界ではよく知られている。
【００１４】
本発明方法においては、円柱状又は円筒状の導電性軸側面周囲に、厚み方向に抵抗値傾斜を有する抵抗物質の抵抗値が低い面を最内層側として備えた抵抗ローラの最外層と、絶縁性基材の一方の主面に備えた強磁性金属薄膜（以下「導電層」ともいう。）とを接触し、前記抵抗ローラの前記導電性軸に電圧を印加し、前記導電層に薄膜を形成する。
【００１５】
本発明方法は、導電層に当接する抵抗ローラを、導電性軸側面に形成する抵抗物質の抵抗値が導電層と当接する抵抗物質の抵抗値より低い抵抗値の傾斜を有するため、導電性軸側面からの抵抗物質中への電流路が抵抗ローラ表面に向かって順次拡大できるため抵抗ローラ内でも電流の集中度合いが是正できると共に、絶縁性基材に備えた導電層と抵抗ローラの抵抗物質との接触箇所における抵抗値の均一化が図れ、電圧を印加しながら導電層の保護膜を形成する際に、導電層及び／又は絶縁性基材に対するジュール熱の発生を拡大均一化でき、これにより保護膜形成時に生じる導電層及び／又は絶縁性基材に対する損傷を抑制することができ、緻密な保護膜を高速に成膜することができる。
【００１６】
また、前記抵抗ローラは、導電層に接触する最外層の固有抵抗値を、１Ω・ｃｍ以上５００Ω・ｃｍ以下の範囲とすることが好ましい。抵抗ローラの最外層の固有抵抗値が１Ω・ｃｍ未満では、抵抗ローラ最外層と導電層との接触箇所が少ない場合でも通電できる傾向が現れ、通電箇所が少ないことにより通電電流が集中し、集中することにより局部的にジュール熱の発生が見受けられ、当該ジュール熱により絶縁性基材及び／又は導電層に欠陥が生じ易いためと想定される欠陥が見受けられるため、抵抗ローラの最外層の固有抵抗値を１Ω・ｃｍ以上が好ましい。また、抵抗ローラの最外層の固有抵抗値が５００Ω・ｃｍを越えると、通電箇所は増加し抵抗ローラの軸方向に亘り導電層への通電は均一化されることが想定されるが、通電箇所における抵抗ローラ自体で発生するジュール熱が大きくなる傾向が見られ、例えば気相堆積法で形成される等の導電層では当該導電層中に含まれる気体の膨張及び／又は導電層からのガス抜けにより、絶縁性基材と導電層との密着強度及び／又は導電層と導電層上に成膜する薄膜との密着強度が低下することで、導電層上に均一な薄膜を形成しがたい場合が発生するため、抵抗ローラの最外層の固有抵抗値は５００Ω・ｃｍ以下が好ましい。従って、抵抗ローラの最外層の固有抵抗値を１Ω・ｃｍ以上５００Ω・ｃｍ以下とすることにより、導電層に強磁性金属を適用した場合に導電層と抵抗ローラ最外層との接触抵抗値の適正化が図れるため、安定した保護膜の形成を可能と成し得る。
【００１７】
また、前記抵抗ローラは、導電性軸側面側の最内層の固有抵抗値が、前記軸側面の固有抵抗値よりも大きく０．１Ω・ｃｍ以下とすることが好ましい。抵抗ローラの最内層の固有抵抗値が０．１Ω・ｃｍを越えると、抵抗ローラの軸方向の端部近傍に通電電流が集中する傾向が見受けられ、抵抗ローラの軸方向の長さによっては抵抗物質の厚み方向の抵抗傾斜だけでは導電層と抵抗ローラの最外層との接触箇所全体に渡り通電を均一化しきれない場合が発生するため、抵抗ローラの最内層の固有抵抗値を軸側面の固有抵抗値よりも大きく０．１Ω・ｃｍ以下とすることにより、抵抗ローラの抵抗物質中の電流路の拡大の適正化が図れ、最外層を通じて導電層への電流供給における集中を抑制でき、安定した保護膜の形成ができる。
【００１８】
また、前記抵抗ローラは、その最大表面粗さを０．０５μｍ以上１μｍ以下の範囲とすることが好ましい。抵抗ローラの最外層の最大表面粗さが０．０５μｍ未満であると、導電層を備えた絶縁性基材と抵抗ローラの最外層との密着度が高くなりすぎ抵抗ローラ最外層上での動きの自由度が低下する、及び／又は、例えば気相堆積法で形成される等の導電層では当該導電層中に含まれる気体が導電層と抵抗ローラ最外層との境界に蓄積する、の何れかにより導電層と抵抗ローラ最外層との密着性が結果的に劣ると想定されるため、抵抗ローラの最外層の最大表面粗さは０．０５μｍ以上が好ましい。また１μｍを越えると導電層と抵抗ローラ最外層との通電箇所が独立する傾向にあるため、及び／又は、導電層表面に抵抗ローラ最外層の形状が転写される傾向にあるため、の何れかにより導電層と抵抗ローラの最外層における通電不良が発生する傾向が見受けられ、抵抗ローラの最外層の最大表面粗さは１μｍ以下が好ましい。
【００１９】
前記抵抗ローラは、円柱状又は円筒状の導電性軸側面を、一方の面の固有抵抗値が前記軸側面の固有抵抗値より大きく０．１Ω・ｃｍ以下で、他方の面の固有抵抗値が１Ω・ｃｍ以上５００Ω・ｃｍ以下の厚み方向に抵抗傾斜を有する抵抗物質で、前記一方の面を前記軸側面に接して覆って形成するのが好ましい。このようにすると、電圧を印加しながら導電層に当該導電層を保護する保護膜を形成する薄膜形成方法に適用する、特に強磁性金属層を保護する保護膜を成膜する薄膜形成方法に適用する場合に、高速で安定な成膜が達成できる。
【００２０】
【実施例】
以下実施例を用いてさらに具体的に説明する。なお、以下に説明する薄膜形成方法は、導電層を強磁性金属薄膜、当該強磁性金属薄膜上に成膜する薄膜を硬質炭素膜とした磁気記録媒体を例に採り、硬質炭素膜をプラズマＣＶＤ法で形成する場合について説明する。
【００２１】
図２は本実施例の磁気記録媒体の基本構造を示す。電気的絶縁性基材１には、３〜２０μｍ厚みを有するポリエチレンテレフタレート（ＰＥＴ）、ポリエチレン-2,6-ナフタレート（ＰＥＮ）、ポリアミド（ＰＡ）、ポリイミド（ＰＩ）等の耐熱可撓性フィルムからなる非磁性基材が好適である。強磁性金属薄膜２は、０．０５〜０．３μｍの膜厚で、Ｃｏ等の強磁性金属を斜方蒸着により酸素を導入しながら形成する。硬質炭素膜３は、強磁性金属薄膜２の表面に形成され、強磁性金属薄膜２を保護する。潤滑剤層４は、硬質炭素膜３の上に形成され、固体潤滑剤等を湿式塗布法又は真空蒸着法で形成する。バックコート層５は、ポリエステル樹脂とカーボン等の潤滑性物質との混合体を、溶媒で希釈し調粘し、湿式塗布することにより形成される。このようにして、本実施例に適用する磁気記録媒体６が得られる。
【００２２】
図１は本発明の薄膜形成方法の一実施例を説明する薄膜形成装置の概略構造であり、硬質炭素膜３を強磁性金属薄膜２の上に形成する。なお、硬質炭素膜３を形成する際には、絶縁非磁性基材（以下、「非磁性基材」という。）１に強磁性金属薄膜２のみを成膜した磁気記録前駆体７、又は、非磁性基材１の一方の面に強磁性金属薄膜２を他の面にバックコート層５を成膜した磁気記録前駆体８の何れでも適用できるが（図２参照）、本実施例では磁気記録前駆体８に硬質炭素膜３を成膜する場合について説明する。
【００２３】
図１において、磁気記録前駆体８は繰出ローラ９に巻かれているとともに、この繰出ローラ９から張力を制御されて送り出される。抵抗ローラ１０及び１１は、装置本体１２と絶縁され、図２に示す強磁性金属薄膜２からの電流を通電する。抵抗ローラ１０は、磁気記録前駆体８の強磁性金属薄膜２と接触して回転する。抵抗ローラ１１は、硬質炭素膜３と接触して回転する。メインローラ１３は、磁気記録前駆体８を一定速度で搬送するように、回転速度を制御されている。なお、本実施例では抵抗ローラ１０及び１１を備えた場合であるが、一方だけでも適用できる。しかしながら、抵抗ローラ１０のみとし、他方を電気導通性ローラ又は絶縁性ローラとし、他方のローラ（図では１１に相当）に電圧を印加しない場合、メインローラ１３及び／又はローラ１１と硬質炭素膜３を成膜した磁気記録前駆体１４との剥離箇所で剥離放電の発生確率が高い場合が発生し、成膜した硬質炭素膜３及び／又は強磁性金属薄膜２に欠陥が生じ易く、電気導通性ローラに電圧を印加する場合、硬質炭素膜３と電気導通性ローラ路とが接触する箇所で電流集中の傾向があり、成膜した硬質炭素膜３及び／又は強磁性金属薄膜２に欠陥が生じ易い。また、抵抗ローラ１１のみとする場合も前記と同様の傾向が観察される。従って、図示したように抵抗ローラ１０及び１１の双方備えることが望ましい。なお、巻取りローラ１５は、硬質炭素膜３形成後の磁気記録前駆体１４を連続的に巻き取るローラであり、繰出ローラ９と同様に張力を制御されている。
【００２４】
放電管１６は、硬質炭素膜３をプラズマＣＶＤ法で成膜するための装置で、内部にプラズマ発生用電極１７を備えている。原料ガス導入口１８から、炭素源（一例として炭素数１〜１２の範囲のアルカン、アルケン、アルキンなどの脂肪族、若しくは脂環族、又は芳香族及びこれらのエーテル、エステルなどを含む誘導体）の反応ガスを単独あるいは水素、窒素、酸素、アルゴン等と混合して（例えば炭素源ガス１ｖｏｌ．％に対して、他のガス０．１〜５ｖｏｌ．％の割合）、１３０〜０．１３Ｐａの圧力で放電管１６内に導入している。電源１９は、電極１７と抵抗ローラ１０及び１１に接続され抵抗ローラ側で接地され、例えば電圧０．５ｋＶ〜７ｋＶの直流、同電圧の１ｋＨｚ〜５ＧＨｚの交流、又はこれらを重畳して用いる。これら、放電管１６，プラズマ発生用電極１７，原料ガス導入口１８，電源１９によりプラズマＣＶＤ法で成膜を行う。
【００２５】
さらに装置本体１２は真空槽であり、真空バルブ２０を介して真空ポンプ２１により真空排気され、装置本体１２の真空度を放電管１６に供給されるガス流量（すなわち、放電管１６内の圧力）に応じて所定値（例えば０．３×１０^-2Ｐａ）になるように真空ポンプ２１の容量を選定する。
【００２６】
図３は抵抗ローラ１０及び１１の構成を示す断面図である。抵抗物質２２と、円筒状の導電性軸側面２３と、導電性軸側面２３と軸２５とを回転自在に支持する軸受２４で構成されている。抵抗物質２２は、固有抵抗値が導電性軸側面２３との接合面から離隔するほど固有抵抗値が高くなっている。すなわち、厚み方向に電気的抵抗値が傾斜するように変化している。抵抗物質２２に用いられる材料としては、例えばカーボン、炭化珪素、酸化チタン（以下、チタニアと称す）、酸化クロム（以下、クロミナと称す）、酸化アルミニウム（以下、アルミナと称す）等が単独又は混合して適用され、例えば図４Ａに示したように固有抵抗値が異なる抵抗物質層２６ａ〜２６ｄを積層し、段階的な抵抗傾斜を備えた抵抗物質２６、又は図４Ｂに示したように固有抵抗値が異なる抵抗物質の混合比率を変化させ連続的な抵抗傾斜を備えた抵抗物質層２７の何れでも良い。抵抗物質層２６ａ〜２６ｄを作成するには、例えばプラズマ溶射を用いて次のように電気的抵抗値を段階的に変化させて形成する（トータル膜厚は０．５〜３ｍｍ）。
２６ａ：すべてチタニア
２６ｂ：チタニア８０質量％とクロミナ又はアルミナ２０質量％
２６ｃ：チタニア５０質量％とクロミナ又はアルミナ５０質量％
２６ｄ：チタニア２０質量％とクロミナ又はアルミナ８０質量％
抵抗物質層２７を作成するには、前記抵抗物質層２６ａ〜２６ｄの段階的変化を連続的変化にさせる。
【００２７】
抵抗物質２２の製造方法としては、例えば溶射法、スパッター法等が適用でき、抵抗傾斜の傾きは絶縁性基材に備えた導電層の抵抗値、当該導電層に流す電流の値、導電層上に成膜する薄膜の膜厚、成膜した薄膜の抵抗値等に応じて適宜設定できる。導電性軸側面２３、軸受２４及び軸２５は共に固有抵抗値が低い電気良導体であり、アルミニウム、銅等の金属単体、ステンレススチール（以下、ステンレスと称す）等の合金、固有抵抗値の低い炭化珪素又はカーボン等が適用できる。抵抗物質２２の固有抵抗値としては、導電性軸側面２３に接する最内層は導電性軸側面２３の固有抵抗値より高く０．１Ω・ｃｍ以下が好ましく、強磁性金属薄膜２又は硬質炭素膜３と接する最外層は１Ω・ｃｍ以上５００Ω・ｃｍ以下が好ましい。また、抵抗ローラ１０及び１１の最外層面の最大表面粗さは０．０５μｍ以上１μｍ以下が好ましい。なお、電流路は、電源１９からプラズマ発生用電極１７を経て、プラズマ電流が磁気記録前駆体８に流れ、強磁性金属薄膜２・抵抗ローラ１０及び１１を介して電源１９に帰還する。これらで構成される電流路は、装置本体１２と絶縁されている。
【００２８】
次に、本発明の薄膜形成方法について図１の装置に基づき説明する。装置本体１２は、真空バルブ２０を開放し、真空ポンプ２１で排気し、規定の真空度（例えば１．３×１０^-2Ｐａ）に到達した後、強磁性金属薄膜２を形成した磁気記録前駆体８をメインローラ１３に密着し、繰出ローラ９から巻取りローラ１５に向けて連続的に送り出されている。繰出ローラ９から繰り出された磁気記録前駆体８はメインローラ１３で放電管１６の開口部（図示は省略）と対向する位置まで搬送され、プラズマＣＶＤの成膜領域に到達する。
【００２９】
プラズマＣＶＤ成膜領域では、電源１９からの電圧とガス導入口１８から原料ガスの供給により、放電管１６内のプラズマ発生用電極１７からプラズマのイオン電流が発生加速され、プラズマ発生用電極１７に対向して位置する強磁性金属薄膜２上に硬質炭素膜３が形成される。このとき強磁性金属薄膜２を流れる電流は、抵抗ローラ１０及び１１の抵抗物質２２で分散通電され、抵抗ローラ１０及び１１の最外層面と強磁性金属薄膜２とが接する箇所の電流が低く抑えられ、抵抗物質２２の内部に流れるに従い当該抵抗物質２２の固有抵抗値は低くなることと、導電性軸側面２３に近くなるほど抵抗物質２２の径も小さくなることとで、抵抗物質２２の厚み方向で流れる電流の集中を行うことができ、すなわち最外層からの電流が分散されたまま導電性軸側面２３に到達し、軸受け２４を介して軸２５に伝達されるため、磁気記録前駆体８と抵抗ローラ１０及び１１との軸２５方向における接触箇所の実測抵抗値がほぼ一定になる。このことにより、極めて均一で、かつ通電欠陥のない硬質炭素膜３を形成することができ、ドロップアウトの低減と耐食性が向上する。
【００３０】
次に、磁気記録前駆体８に硬質炭素膜３を成膜した例を挙げ、本発明をさらに詳細に説明する。非磁性絶縁基材１として、幅５００ｍｍ、厚さ６μｍのＰＥＴフィルムを用い、一方の面に斜方蒸着法によりＣｏ−Ｏからなる強磁性金属薄膜２を厚み０．１２μｍで形成した。他方の面にはバックコート層５を、湿式塗布法により乾燥厚みで０．５μｍの厚さに形成し、磁気記録前駆体８を得た。前記バックコート層５は、まずフィラー（充填材）として平均粒子径約６０ｎｍのカーボンブラックと平均粒子径約６０ｎｍの炭酸カルシウムを質量比２：８（カーボンブラック：炭酸カルシウム）と、バインダー樹脂としてポリエステル樹脂とニトロセルロースを質量比１：１（ポリエステル樹脂：ニトロセルロース）とを、フィラー：バインダー樹脂＝２：１（質量比）となるように計り取り、これを１５質量％とし、これに溶媒（トルエン５０vol.%、メチルエチルケトン２５vol.%、シクロヘキサノン２５vol.%）を８５質量％となるように加えて混合し、グラビアコーターで塗布し、溶媒を乾燥させて形成した。
【００３１】
前記のようにして作製した磁気記録前駆体８の強磁性金属薄膜２の表面に、抵抗ローラ１０及び１１の抵抗物質２２の材料及び／又は固有抵抗値を代えて硬質炭素膜３を成膜、抵抗ローラ１０及び１１の導電性軸側面２３の材料及び／又は固有抵抗値を代えて硬質炭素膜３を成膜、及び抵抗ローラ１０及び１１の最外層の最大表面粗さを代えて硬質炭素膜３を成膜し、磁気記録前駆体１４を得た。
【００３２】
具体的には、ヘキサンガス対アルゴンガスを体積比で３対１に混合し、総ガス圧１０５Ｐａで原料ガス導入口１８から放電管１６に供給し、プラズマ発生用電極１７に電源１９から電圧１．２ｋＶ、２アンペアの直流を印加し、強磁性金属薄膜２上に硬質炭素膜３を１０ｎｍ形成する条件を一定として、抵抗ローラ１０及び１１をセットで代えて、試料Ｎｏ．１０１〜１１８を作製した。
【００３３】
本実施例で用いた抵抗ローラ１０及び１１の抵抗物質２２と導電性軸側面２３との材料を（表１）に、抵抗ローラ１０及び１１の抵抗物質２２の最外層、最内層、導電性軸側面２３それぞれの固有抵抗値、及び抵抗物質２２の最外層の最大表面粗さを、後述する評価結果と共に（表２）に示す。なお、抵抗ローラ１０及び１１は何れも最内層の固有抵抗値から最外層の固有抵抗値までを３層積層して形成し、２層目の固有抵抗値は最内層の固有抵抗値と最外層の固有抵抗値との中間の値を適用し、それぞれの厚みを１ｍｍ、総厚み３ｍｍとしてプラズマ溶射で作製した。
【００３４】
抵抗傾斜を有する抵抗ローラ１０及び１１に代え、比較として導電性軸側面からローラ最外層まで同一物質で形成したローラ、及び導電性軸側面に用いた材料と異なるが抵抗傾斜を備えない材料を当該導電性軸側面周囲に備えるローラを適用し、前記と同一の条件で強磁性金属薄膜２に硬質炭素膜３を成膜した試料Ｎｏ．２０１〜２０９を作製した。試料Ｎｏ．２０１〜２０９それぞれに用いた材料を（表１）に、また固有抵抗値、ローラの最大表面粗さ（Ｒmax）、及び成膜した硬質炭素膜３のドロップアウトとスチル寿命の評価結果を（表２）に示す。
【００３５】
【表１】

【００３６】
前記の試料Ｎｏ．１０１〜１１８及び２０１〜２０９のローラで成膜した硬質炭素膜３の膜質を評価するため、次に示す評価実験を行った。磁気記録前駆体１４の硬質炭素膜３の表面に、潤滑剤層４として下記化学式（化１）に示す含フッ素カルボン酸アミン塩を厚さ約４ｎｍに湿式塗布法で形成し、６．３５ｍｍ幅に裁断し磁気記録媒体６を作製した。このコーティングは、テトラヒドロフラン等の溶媒に溶かして塗布し、乾燥した。下記化学式（化１）に示す含フッ素カルボン酸アミン塩とその合成方法は、米国特許5,604,032号明細書、EPC 0652206B1号明細書により知られている。
【００３７】
【化１】

【００３８】
その後、ディジタルビデオカメラ（以下、ＤＶＣと称す）カセットに１０ｍ程度装着し、市販のＤＶＣ一体型ビデオテープレコーダ（松下電器産業社製商品名“ＮＶ−ＧＳ２７”：ヘリカルスキャン型で小径シリンダーを搭載したビデオテープレコーダ）のヘッド出力を外部に取り出せるように改造して、３μｓｅｃ、６ｄＢのドロップアウトを、温度：２３℃、相対湿度：７０％の環境下で１０分間測定し、１分間の平均個数を測定値とし、２００個以下を合格とした。なお、この測定は幅方向１０点測定し最も多い箇所の値を採用した。また、耐食性の評価は、約７０ｍ長の磁気記録媒体６を、ドロップアウト測定と同様のＤＶＣカセットとＤＶＣ一体型ビデオテープレコーダを用いて、温度：２３℃、相対湿度：７０％の環境下で信号を記録し、温度：６０℃、相対湿度：９０％の環境下に１０日放置した後、温度：２３℃、相対湿度：１０％の環境下でのスチル寿命を測定し、１０分以上を合格した。
【００３９】
【表２】

【００４０】
最外層の固有抵抗値については、固有抵抗値が高いほどドロップアウトの改善効果が見られ、試料Ｎｏ．２０１〜２０３と比較すると、１Ω・ｃｍ以上でその効果が現れ、試料Ｎｏ．２０９と試料Ｎｏ．１１８とを比較すると最外層の固有抵抗値は、５００Ω・ｃｍ以下が好ましいことが分かる。この最外層の固有抵抗値に適切な範囲が存在する原因については定かではないが、次のような点が想定される。すなわち、最外層の固有抵抗値が低いと、通電時に少ない通電点で足りるため、１点当りの電流密度が大きくなり、ジュール熱で非磁性絶縁基材１又は強磁性薄膜２を損傷又は欠陥が生じ、記録再生欠陥が増加（すなわち、ドロップアウトの値が大きくなる）すると共に、強磁性金属薄膜２の欠陥部に成膜された硬質炭素３にピンホールが発生し、硬質炭素膜３のピンホールから強磁性金属薄膜２が錆びるためと考えられる。逆に最外層の固有抵抗値が高いと、通電点が多くなるが通電点１点当たりの抵抗が大きくなり、抵抗ローラ１０及び／又は１１が発熱し、気相堆積法で成膜した強磁性金属薄膜２中に含まれるガスがアウトガスとして発生し、硬質炭素膜３と強磁性金属薄膜２との密着強度がやや低下する傾向にあるためではないかと考えられる。
【００４１】
また、最内層の固有抵抗値については、抵抗値が高くなると抵抗ローラ１０及び１１の軸方向全体に亘り通電電流が強磁性金属薄膜２に流れ難く、抵抗ローラ１０及び１１の軸方向の端部にやや集中するため、記録再生欠陥がやや増加する傾向にあると考えられ、０．１Ω・ｃｍ以下が適切である。また、最内層の固有抵抗値は導電性軸側面２３よりも大きい物質であれば良く、導電性軸側面２３の固有抵抗値に近ければ近いほど電源１９からの通電抵抗が抑制できるが、抵抗ローラ１０及び１１の最外層の固有抵抗値と抵抗物質２２の厚みの兼ね合いで適宜選択して用いられる。
【００４２】
さらに、抵抗ローラ１０及び１１の最外層の最大表面粗さについては、大きくなると表面形状が強磁性金属薄膜２及び／又は非磁性絶縁基材１に転写されるため、又は抵抗ローラ１０及び１１の最外層と強磁性金属薄膜２との通電箇所が独立した点状になるための何れかにより均一な通電を確保しにくく、記録再生欠陥が増加傾向になり、小さすぎると耐食性に劣る（すなわち、スチルが低下する）原因は、抵抗ローラ１０及び１１表面で強磁性金属薄膜２を備えた非磁性絶縁基材１が自由に移動できなくなることによって密着強度が低下するのか、強磁性金属薄膜２中に内包されている気体成分が強磁性金属薄膜２と抵抗ローラ１０及び１１との接触界面からアウトガスとして抜け切らないためか、どちらかの原因ではないかと考えられ、０．０５〜１．０μｍの範囲が適切である。
【００４３】
何れにしても、上記理由の何れかであるため、（表２）から明らかなように、本発明に係る試料Ｎｏ．１０１〜１１８は試料Ｎｏ．２０１〜２０９に比べると記録再生欠陥（ドロップアウトで評価）及び耐食性（スチルで評価）共に大幅な改善が見られる。特に導電性軸側面からローラの最外層まで同一の材料で形成した試料Ｎｏ．２０１〜２０４と比較すると、評価特性の向上効果は顕著である。
【００４４】
なお、磁気記録媒体について詳しい説明をしたが、本発明は、導電体と絶縁層を有する半導体、プリント基板、液晶の導電膜の形成にも応用できる。
【００４５】
【発明の効果】
以上説明したように本発明によれば、絶縁性基材に備えた導電層の上に成膜する薄膜の膜質及び均一性を向上させることができる。特に磁気記録媒体の強磁性金属薄膜上に成膜する硬質炭素膜に適用すると、微少な異常放電及び／又は通電欠陥により磁気記録再生特性を低下させる欠点を撲滅し、磁気記録特性、耐環境性、信頼性、高速成膜性に優れるという顕著な効果がある。
【図面の簡単な説明】
【図１】本発明の薄膜形成方法を用いた装置の一実施例の概念構成図である。
【図２】同、磁気記録媒体の構成を示す概念断面図である。
【図３】同、抵抗ローラの構造を示す断面図である。
【図４】Ａは同、抵抗物質の構成一例を説明する断面図、Ｂは同、抵抗物質の構成の別の例を説明する断面図である。
【符号の説明】
１絶縁非磁性基材（非磁性基材）
２強磁性金属薄膜
３硬質炭素膜
４潤滑剤層
５バックコート層
６磁気記録媒体
７，１４磁気記録前駆体
８磁気記録前駆体
９繰出ローラ
１０，１１抵抗ローラ
１２装置本体（真空槽）
１３メインローラ
１６放電管
１７プラズマ発生用電極
１８原料ガス導入口
１９電源
２０真空バルブ
２１真空ポンプ
２２抵抗物質
２３導電性軸側面
２４軸受
２５軸
２６ａ〜２６ｄ抵抗物質層
２７抵抗物質層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium in which a hard carbon film is formed on the surface of a ferromagnetic metal thin film provided on an insulating substrate, a manufacturing method thereof, and a manufacturing apparatus thereof.
[0002]
[Prior art]
With the recent increase in recording density in the magnetic recording field in the information recording field, the performance of not only the recording film but also the protective film that protects the recording film is one of the important basic technologies that determine the reliability of the product. Further, in order to provide a magnetic recording medium at a low cost, it is also essential to form a recording film and a protective film at high speed. High-speed film formation technology for recording films has been established with the progress of vacuum deposition, but since the protective film is required to cover the entire surface of the recording film without any defects, a precise film formation method is required. Alternatively, a plasma CVD (chemical vapor deposition) method has been studied.
[0003]
As a method for forming the protective film, a plasma CVD method having a high film formation rate is advantageous for high-speed film formation, and various proposals have been made. In order to improve the film quality formed by the plasma CVD method and to ensure reliability, film formation with high energy is essential. However, since film formation with high energy requires high current, it is necessary to increase the energization point of the resistance roller itself that supplies current to the recording film.
[0004]
In a commonly used metal roller, since the resistance value at the contact point is extremely low, the current value per point becomes high, and Joule heat is generated due to the contact resistance at the contact point and / or the resistance value of the recording film. The Joule heat causes damage to the insulating base material and / or the recording film and defects in the protective film itself, and these defects cause recording / reproducing defects on the recording film. Furthermore, when a medium having the above-mentioned defects is left in a high-temperature and high-humidity environment, rust with any of these defects as the core is generated in the recording film, and the reliability such that recording or reproduction becomes impossible is significantly reduced. The problem of making it occur. In response to this problem, a technique for supplying current via a resistance roller having a surface resistance value optimized for a recording film when forming a protective film has been proposed, and the reliability of a magnetic recording medium suitable for general use is proposed. Sexuality has been resolved.
[0005]
However, in severe use conditions, for example, a video tape recorder equipped with a helical scan type high-speed rotating small-diameter cylinder, there is a problem that dropout or error rate due to a minute defect increases. In addition, after storage in a high-temperature and high-humidity environment, there is a problem in that dropout is greatly increased due to a decrease in adhesion strength to the recording film and film quality of the protective film. As an example of a video tape recorder equipped with a helical scan type small diameter cylinder, the following Patent Document 1 is proposed.
[0006]
[Patent Document 1]
JP-A-4-236588
[0007]
[Problems to be solved by the invention]
In order to solve the above-described conventional problems, an object of the present invention is to provide a magnetic recording medium that can maintain high reliability even for more severe applications, a manufacturing method thereof, and a manufacturing apparatus thereof.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the magnetic recording medium of the present inventionThe method of manufacturing a magnetic recording medium includes a ferromagnetic metal thin film, a hard carbon film, and a lubricant layer in this order on the surface of an electrically insulating film, and a back coating layer on the back surface. The outermost layer of the resistance roller having an electric resistance value gradient in the thickness direction around the conductive axis and the lower electric resistance value as the innermost layer side and the higher electric resistance value as the outermost layer side And a surface of the ferromagnetic metal thin film by plasma CVD using a hydrocarbon reactive gas supplied to a vacuum tank while applying a voltage to the conductive axis of the resistance roller. A carbon film is formed.
[0010]
Next, the magnetic recording medium manufacturing apparatus according to the present invention supplies a hydrocarbon reaction gas to a decompression tank equipped with a resistance roller and plasma CVD to form the surface of the ferromagnetic metal thin film formed on the surface of the insulating film. An apparatus for producing a magnetic recording medium by forming a hard carbon film on the resistance roller, wherein the resistance roller has an electric resistance value inclined in the thickness direction, and the electric resistance value is the innermost layer side. A surface having a high resistance value is the outermost layer side, and a conductive shaft for applying a voltage to the shaft of the resistance roller is provided.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a dropout value of 200 or less means that there are few recording / reproducing defects. Moreover, that a still life is 10 minutes or more means that corrosion resistance is high. Therefore, the magnetic recording medium of the present invention has characteristics of few recording / reproducing defects and high corrosion resistance.
[0012]
In the present invention, the hard carbon film preferably has a thickness of 5 nm to 30 nm, more preferably 8 to 15 nm, on the surface of the ferromagnetic metal thin film. Within the above range, dense and uniform recording is possible. Here, the hard carbon film is amorphous carbon and is also called a diamond-like carbon film.
[0013]
In addition, the ferromagnetic metal thin film is preferably formed by introducing ferromagnetic metal containing Co oxide while introducing oxygen by oblique vapor deposition. Other examples of the ferromagnetic metal thin film include Co—Ni—O, Co—Ni—Cr, and Co—Cr. The thickness of the ferromagnetic metal thin film is preferably in the range of 0.05 to 0.3 μm. Oblique deposition is well known in the art.
[0014]
In the method of the present invention, the outermost layer of the resistance roller provided with a surface having a low resistance value having a resistance value gradient in the thickness direction as the innermost layer side around the side surface of the columnar or cylindrical conductive shaft, A ferromagnetic metal thin film (hereinafter also referred to as “conductive layer”) provided on one main surface of the conductive substrate, a voltage is applied to the conductive axis of the resistance roller, and the thin film is applied to the conductive layer. Form.
[0015]
In the method of the present invention, since the resistance value of the resistance material formed on the side surface of the conductive shaft is lower than the resistance value of the resistance material in contact with the conductive layer, the resistance roller in contact with the conductive layer has a slope of the resistance value. Since the current path from the side surface to the resistance material can be expanded gradually toward the resistance roller surface, the concentration of current can be corrected in the resistance roller, and the conductive layer provided on the insulating substrate and the resistance material of the resistance roller The resistance value at the contact point can be made uniform, and when the protective film of the conductive layer is formed while applying a voltage, the generation of Joule heat on the conductive layer and / or the insulating substrate can be enlarged and uniformed. It is possible to suppress damage to the conductive layer and / or the insulating base material that occurs during the formation of the protective film, and a dense protective film can be formed at a high speed.
[0016]
The resistance roller preferably has a specific resistance value of an outermost layer in contact with the conductive layer in a range of 1 Ω · cm to 500 Ω · cm. If the specific resistance value of the outermost layer of the resistance roller is less than 1 Ω · cm, there is a tendency to energize even when there are few contact points between the outermost layer of the resistance roller and the conductive layer. As a result, the generation of Joule heat is observed locally, and defects assumed to be likely to occur in the insulating base material and / or conductive layer due to the Joule heat are found. The resistance value is preferably 1 Ω · cm or more. In addition, if the specific resistance value of the outermost layer of the resistance roller exceeds 500 Ω · cm, it is assumed that the number of energized locations increases and the energization to the conductive layer is made uniform in the axial direction of the resistance roller. The Joule heat generated in the resistance roller itself tends to increase. For example, in a conductive layer formed by a vapor deposition method, the gas contained in the conductive layer expands and / or the gas escapes from the conductive layer. If the adhesion strength between the insulating substrate and the conductive layer and / or the adhesion strength between the conductive layer and the thin film formed on the conductive layer is reduced, it is difficult to form a uniform thin film on the conductive layer. Therefore, the specific resistance value of the outermost layer of the resistance roller is preferably 500 Ω · cm or less. Therefore, by setting the specific resistance value of the outermost layer of the resistance roller to 1 Ω · cm to 500 Ω · cm, when the ferromagnetic metal is applied to the conductive layer, the contact resistance value between the conductive layer and the outermost layer of the resistance roller is appropriate. Therefore, a stable protective film can be formed.
[0017]
Further, in the resistance roller, it is preferable that the specific resistance value of the innermost layer on the conductive shaft side surface side is larger than the specific resistance value of the shaft side surface and is 0.1 Ω · cm or less. When the specific resistance value of the innermost layer of the resistance roller exceeds 0.1 Ω · cm, there is a tendency for current to concentrate near the end of the resistance roller in the axial direction. Depending on the length of the resistance roller in the axial direction, Since there is a case where the current cannot be made uniform over the entire contact area between the conductive layer and the outermost layer of the resistance roller only by the resistance gradient in the thickness direction of the material, the specific resistance value of the innermost layer of the resistance roller is set to the specific resistance of the shaft side surface. By setting the resistance value to 0.1Ω · cm or less larger than the resistance value, it is possible to optimize the expansion of the current path in the resistance material of the resistance roller, and the concentration in the current supply to the conductive layer through the outermost layer can be suppressed and stable. A protective film can be formed.
[0018]
The resistance roller preferably has a maximum surface roughness in a range of 0.05 μm to 1 μm. When the maximum surface roughness of the outermost layer of the resistance roller is less than 0.05 μm, the degree of adhesion between the insulating base material provided with the conductive layer and the outermost layer of the resistance roller becomes too high, and the movement on the outermost layer of the resistance roller. And / or in a conductive layer formed by vapor deposition, for example, gas contained in the conductive layer accumulates at the boundary between the conductive layer and the outermost layer of the resistance roller. Therefore, it is assumed that the adhesion between the conductive layer and the outermost layer of the resistance roller is inferior as a result. Therefore, the maximum surface roughness of the outermost layer of the resistance roller is preferably 0.05 μm or more. If the thickness exceeds 1 μm, either the current-carrying portion of the conductive layer and the outermost layer of the resistance roller tends to be independent, and / or the shape of the outermost layer of the resistance roller tends to be transferred to the surface of the conductive layer. As a result, there is a tendency that a conduction failure occurs in the outermost layer of the conductive layer and the resistance roller, and the maximum surface roughness of the outermost layer of the resistance roller is preferably 1 μm or less.
[0019]
The resistance roller has a columnar or cylindrical conductive shaft side surface, the specific resistance value of one surface is larger than the specific resistance value of the shaft side surface and is 0.1 Ω · cm or less, and the specific resistance value of the other surface is It is preferable to form a resistance substance having a resistance gradient in a thickness direction of 1 Ω · cm or more and 500 Ω · cm or less and covering the one surface in contact with the side surface of the shaft. In this way, the present invention is applied to a thin film forming method for forming a protective film for protecting the conductive layer on the conductive layer while applying a voltage, particularly to a thin film forming method for forming a protective film for protecting the ferromagnetic metal layer. In this case, high-speed and stable film formation can be achieved.
[0020]
【Example】
Hereinafter, it demonstrates more concretely using an Example. The thin film formation method described below takes as an example a magnetic recording medium in which a conductive layer is a ferromagnetic metal thin film and a thin film formed on the ferromagnetic metal thin film is a hard carbon film. The case of forming by the method will be described.
[0021]
FIG. 2 shows the basic structure of the magnetic recording medium of this embodiment. The electrically insulating substrate 1 is made of heat-resistant flexible film such as polyethylene terephthalate (PET), polyethylene-2,6-naphthalate (PEN), polyamide (PA), polyimide (PI), etc. having a thickness of 3 to 20 μm. The nonmagnetic base material which becomes is suitable. The ferromagnetic metal thin film 2 has a thickness of 0.05 to 0.3 μm and is formed while introducing a ferromagnetic metal such as Co by oblique vapor deposition. The hard carbon film 3 is formed on the surface of the ferromagnetic metal thin film 2 and protects the ferromagnetic metal thin film 2. The lubricant layer 4 is formed on the hard carbon film 3, and a solid lubricant or the like is formed by a wet coating method or a vacuum deposition method. The back coat layer 5 is formed by diluting a mixture of a polyester resin and a lubricious substance such as carbon with a solvent, adjusting the viscosity, and applying the mixture wet. In this way, the magnetic recording medium 6 applied to this embodiment is obtained.
[0022]
FIG. 1 shows a schematic structure of a thin film forming apparatus for explaining an embodiment of a thin film forming method of the present invention, in which a hard carbon film 3 is formed on a ferromagnetic metal thin film 2. When the hard carbon film 3 is formed, the magnetic recording precursor 7 in which only the ferromagnetic metal thin film 2 is formed on the insulating nonmagnetic base material (hereinafter referred to as “nonmagnetic base material”) 1, or Any of the magnetic recording precursors 8 in which the ferromagnetic metal thin film 2 is formed on one surface of the nonmagnetic substrate 1 and the backcoat layer 5 is formed on the other surface can be applied (see FIG. 2). The case where the hard carbon film 3 is formed on the recording precursor 8 will be described.
[0023]
In FIG. 1, the magnetic recording precursor 8 is wound around a feeding roller 9 and is fed out from the feeding roller 9 with tension controlled. The

resistance rollers

10 and 11 are insulated from the apparatus main body 12 and energize the current from the ferromagnetic metal thin film 2 shown in FIG. The resistance roller 10 rotates in contact with the ferromagnetic metal thin film 2 of the magnetic recording precursor 8. The resistance roller 11 rotates in contact with the hard carbon film 3. The rotation speed of the main roller 13 is controlled so that the magnetic recording precursor 8 is conveyed at a constant speed. In this embodiment, the

resistance rollers

10 and 11 are provided, but only one of them can be applied. However, when only the resistance roller 10 is used and the other is an electrically conductive roller or an insulating roller and no voltage is applied to the other roller (corresponding to 11 in the figure), the main roller 13 and / or the roller 11 and the hard carbon film 3 are used. There is a case where the probability of occurrence of peeling discharge is high at the peeling position from the magnetic recording precursor 14 on which the film is formed, and the hard carbon film 3 and / or the ferromagnetic metal thin film 2 is likely to be defective, and the electrical conductivity. When a voltage is applied to the roller, there is a tendency of current concentration at the place where the hard carbon film 3 and the electrically conductive roller path are in contact with each other, and a defect occurs in the formed hard carbon film 3 and / or the ferromagnetic metal thin film 2. easy. Further, when only the resistance roller 11 is used, the same tendency as described above is observed. Therefore, it is desirable to provide both

resistance rollers

10 and 11 as shown. The take-up roller 15 is a roller for continuously taking up the magnetic recording precursor 14 after the hard carbon film 3 is formed, and the tension is controlled in the same manner as the feed roller 9.
[0024]
The discharge tube 16 is an apparatus for forming the hard carbon film 3 by plasma CVD, and includes a plasma generating electrode 17 therein. From the source gas inlet 18, a carbon source (as an example, aliphatics such as alkanes, alkenes and alkynes having 1 to 12 carbon atoms, or alicyclics, or aromatics and derivatives thereof including ethers, esters, etc.) A pressure of 130 to 0.13 Pa when the reaction gas is used alone or mixed with hydrogen, nitrogen, oxygen, argon or the like (for example, a ratio of 0.1 to 5 vol.% Of other gas with respect to 1 vol.% Of the carbon source gas). Is introduced into the discharge tube 16. The power source 19 is connected to the electrode 17 and the

resistance rollers

10 and 11 and is grounded on the resistance roller side. For example, a DC voltage of 0.5 kV to 7 kV, an AC voltage of 1 kHz to 5 GHz, or a combination of these is used. These discharge tube 16, plasma generating electrode 17, source gas inlet 18, and power source 19 are used to form a film by plasma CVD.
[0025]
Further, the apparatus main body 12 is a vacuum tank, and is evacuated by a vacuum pump 21 through a vacuum valve 20, and the gas flow rate at which the degree of vacuum of the apparatus main body 12 is supplied to the discharge tube 16 (ie, the pressure in the discharge tube 16). According to a predetermined value (for example, 0.3 × 10^-2The capacity of the vacuum pump 21 is selected so as to be Pa).
[0026]
FIG. 3 is a cross-sectional view showing the configuration of the

resistance rollers

10 and 11. The resistance material 22, a cylindrical conductive shaft side surface 23, and a bearing 24 that rotatably supports the conductive shaft side surface 23 and the shaft 25. The resistance material 22 has a higher specific resistance value as the specific resistance value is separated from the joint surface with the conductive shaft side surface 23. That is, the electrical resistance value changes so as to incline in the thickness direction. As the material used for the resistance substance 22, for example, carbon, silicon carbide, titanium oxide (hereinafter referred to as titania), chromium oxide (hereinafter referred to as chromina), aluminum oxide (hereinafter referred to as alumina) or the like is used alone or in combination. For example, as shown in FIG. 4A, the resistance material layers 26a to 26d having different specific resistance values are stacked, and the resistance material 26 having a stepwise resistance gradient, or the specific resistance as shown in FIG. 4B. Any of the resistive material layers 27 having a continuous resistance gradient by changing the mixing ratio of the resistive materials having different values may be used. In order to create the resistive material layers 26a to 26d, for example, plasma spraying is used to change the electrical resistance value stepwise as follows (total film thickness is 0.5 to 3 mm).
26a: All titania
26b: 80% by mass of titania and 20% by mass of chromina or alumina
26c: 50% by mass of titania and 50% by mass of chromina or alumina
26d: 20% by mass of titania and 80% by mass of chromina or alumina
In order to form the resistive material layer 27, the stepwise change of the resistive material layers 26a to 26d is changed continuously.
[0027]
As a manufacturing method of the resistance substance 22, for example, a spraying method, a sputtering method, or the like can be applied. The inclination of the resistance slope is the resistance value of the conductive layer provided on the insulating base, the value of the current flowing through the conductive layer, The film thickness can be appropriately set according to the film thickness of the thin film formed, the resistance value of the formed thin film, and the like. The conductive shaft side surface 23, the bearing 24, and the shaft 25 are all good electrical conductors with low specific resistance values, such as single metals such as aluminum and copper, alloys such as stainless steel (hereinafter referred to as stainless steel), and carbonized with low specific resistance values. Silicon or carbon can be applied. As the specific resistance value of the resistive material 22, the innermost layer in contact with the conductive shaft side surface 23 is preferably higher than the specific resistance value of the conductive shaft side surface 23 and 0.1 Ω · cm or less, and the ferromagnetic metal thin film 2 or the hard carbon film 3. The outermost layer in contact with is preferably 1 Ω · cm to 500 Ω · cm. The maximum surface roughness of the outermost layer surfaces of the

resistance rollers

10 and 11 is preferably 0.05 μm or more and 1 μm or less. In the current path, the plasma current flows from the power source 19 through the plasma generating electrode 17 to the magnetic recording precursor 8 and returns to the power source 19 via the ferromagnetic metal thin film 2 and the

resistance rollers

10 and 11. The current path constituted by these is insulated from the apparatus main body 12.
[0028]
Next, the thin film forming method of the present invention will be described based on the apparatus shown in FIG. The apparatus main body 12 opens the vacuum valve 20 and evacuates it with a vacuum pump 21, and a prescribed degree of vacuum (for example, 1.3 × 10 6).^-2After reaching Pa), the magnetic recording precursor 8 on which the ferromagnetic metal thin film 2 is formed is brought into close contact with the main roller 13 and continuously fed from the feeding roller 9 toward the winding roller 15. The magnetic recording precursor 8 fed from the feeding roller 9 is conveyed by the main roller 13 to a position facing the opening (not shown) of the discharge tube 16 and reaches the film formation region of plasma CVD.
[0029]
In the plasma CVD film forming region, the plasma ion current is generated and accelerated from the plasma generating electrode 17 in the discharge tube 16 by the voltage from the power source 19 and the supply of the raw material gas from the gas inlet 18. A hard carbon film 3 is formed on the opposing ferromagnetic metal thin film 2. At this time, the current flowing through the ferromagnetic metal thin film 2 is dispersedly energized by the resistance material 22 of the

resistance rollers

10 and 11, and the current at the portion where the outermost surface of the

resistance rollers

10 and 11 and the ferromagnetic metal thin film 2 are in contact with each other is kept low. As the resistance material 22 flows into the resistance material 22, the specific resistance value of the resistance material 22 decreases and the diameter of the resistance material 22 decreases as the resistance material 22 is closer to the conductive side surface 23. In other words, the current from the outermost layer reaches the conductive shaft side surface 23 while being dispersed, and is transmitted to the shaft 25 via the bearing 24, so that the magnetic recording precursor 8 and The actually measured resistance value of the contact portion in the direction of the axis 25 with the

resistance rollers

10 and 11 becomes substantially constant. This makes it possible to form a hard carbon film 3 that is extremely uniform and free from energization defects, thereby reducing dropout and improving corrosion resistance.
[0030]
Next, the present invention will be described in more detail by giving an example in which the hard carbon film 3 is formed on the magnetic recording precursor 8. A PET film having a width of 500 mm and a thickness of 6 μm was used as the nonmagnetic insulating substrate 1, and a ferromagnetic metal thin film 2 made of Co—O was formed on one surface by an oblique vapor deposition method with a thickness of 0.12 μm. On the other side, the back coat layer 5 was formed to a thickness of 0.5 μm by a wet coating method to obtain a magnetic recording precursor 8. The back coat layer 5 is composed of carbon black having an average particle size of about 60 nm and calcium carbonate having an average particle size of about 60 nm as a filler (filler) in a mass ratio of 2: 8 (carbon black: calcium carbonate) and polyester as a binder resin. Resin and nitrocellulose were weighed at a mass ratio of 1: 1 (polyester resin: nitrocellulose) so that the ratio of filler: binder resin = 2: 1 (mass ratio) was 15% by mass. Toluene 50 vol.%, Methyl ethyl ketone 25 vol.%, Cyclohexanone 25 vol.%) Were added and mixed so as to be 85% by mass, applied with a gravure coater, and the solvent was dried to form.
[0031]
A hard carbon film 3 is formed on the surface of the ferromagnetic metal thin film 2 of the magnetic recording precursor 8 produced as described above, instead of the material of the resistance material 22 and / or the specific resistance value of the

resistance rollers

10 and 11. The hard carbon film 3 is formed by changing the material and / or the specific resistance value of the conductive shaft side surface 23 of the

resistance rollers

10 and 11, and the hard carbon film is changed by changing the maximum surface roughness of the outermost layers of the

resistance rollers

10 and 11. 3 was formed into a magnetic recording precursor 14.
[0032]
Specifically, hexane gas to argon gas is mixed at a volume ratio of 3 to 1, and supplied to the discharge tube 16 from the source gas inlet 18 at a total gas pressure of 105 Pa, and the voltage 1 from the power source 19 is supplied to the plasma generating electrode 17. .2 kV, 2 amperes of direct current is applied, the conditions for forming the hard carbon film 3 to 10 nm on the ferromagnetic metal thin film 2 are constant, and the

resistance rollers

10 and 11 are replaced with a set. 101-118 were produced.
[0033]
The materials of the resistance material 22 and the conductive shaft side surface 23 of the

resistance rollers

10 and 11 used in this embodiment are shown in Table 1, and the outermost layer, the innermost layer, and the conductive shaft of the resistance material 22 of the

resistance rollers

10 and 11 are used. The specific resistance value of each of the side surfaces 23 and the maximum surface roughness of the outermost layer of the resistive material 22 are shown in (Table 2) together with the evaluation results described later. Each of the

resistance rollers

10 and 11 is formed by laminating three layers from the specific resistance value of the innermost layer to the specific resistance value of the outermost layer, and the specific resistance value of the second layer is the specific resistance value of the innermost layer and the outermost layer. A value intermediate between the specific resistance values was applied, and the thickness was 1 mm and the total thickness was 3 mm.
[0034]
Instead of the

resistance rollers

10 and 11 having a resistance gradient, for comparison, a roller formed of the same material from the conductive shaft side surface to the outermost layer of the roller, and a material that is different from the material used for the conductive shaft side surface but does not have a resistance gradient are concerned. Applying a roller provided around the side surface of the conductive shaft, sample No. 1 in which the hard carbon film 3 was formed on the ferromagnetic metal thin film 2 under the same conditions as described above. 201-209 were produced. Sample No. The materials used for each of 201 to 209 are shown in (Table 1), and the specific resistance value, the maximum surface roughness (Rmax) of the roller, and the evaluation results of the dropout and still life of the hard carbon film 3 formed are shown in (Table 1). Shown in 2).
[0035]
[Table 1]

[0036]
Sample No. In order to evaluate the film quality of the hard carbon film 3 formed by the rollers 101 to 118 and 201 to 209, the following evaluation experiment was performed. On the surface of the hard carbon film 3 of the magnetic recording precursor 14, a fluorine-containing carboxylic acid amine salt represented by the following chemical formula (Chemical Formula 1) is formed as a lubricant layer 4 to a thickness of about 4 nm by a wet coating method, and has a width of 6.35 mm. The magnetic recording medium 6 was produced. This coating was applied by dissolving in a solvent such as tetrahydrofuran and dried. A fluorine-containing carboxylic acid amine salt represented by the following chemical formula (Chemical Formula 1) and its synthesis method are known from US Pat. No. 5,604,032 and EPC 0652206B1.
[0037]
[Chemical 1]

[0038]
After that, about 10 m was mounted on a digital video camera (hereinafter referred to as DVC) cassette, and a commercially available DVC integrated video tape recorder (trade name “NV-GS27” manufactured by Matsushita Electric Industrial Co., Ltd .: helical scan type with a small diameter cylinder mounted. Video tape recorder) The head output of the video tape recorder is modified so that it can be taken out. The dropout of 3μsec and 6dB is measured for 10 minutes in an environment of temperature: 23 ° C and relative humidity: 70%. It was set as a measured value, and 200 or less was set as the pass. In this measurement, 10 points in the width direction were measured, and the values at the most points were adopted. Corrosion resistance was evaluated using a magnetic recording medium 6 having a length of about 70 m under the environment of a temperature of 23 ° C. and a relative humidity of 70% using a DVC cassette and a DVC integrated video tape recorder similar to the dropout measurement. Record the signal, leave it for 10 days in an environment of temperature: 60 ° C and relative humidity: 90%, then measure the still life in an environment of temperature: 23 ° C and relative humidity: 10%, passed it.
[0039]
[Table 2]

[0040]
As for the specific resistance value of the outermost layer, the higher the specific resistance value, the better the dropout effect. Compared with 201-203, the effect appears at 1 Ω · cm or more. 209 and Sample No. Comparing with 118, it is understood that the specific resistance value of the outermost layer is preferably 500 Ω · cm or less. The reason for the existence of an appropriate range in the specific resistance value of the outermost layer is not clear, but the following points are assumed. That is, when the specific resistance value of the outermost layer is low, a small energization point is sufficient at the time of energization, so the current density per point increases, and the nonmagnetic insulating substrate 1 or the ferromagnetic thin film 2 is damaged or defective by Joule heat. As a result, the number of recording / reproducing defects increases (that is, the dropout value increases), and a pinhole is generated in the hard carbon 3 formed in the defective portion of the ferromagnetic metal thin film 2. This is probably because the ferromagnetic metal thin film 2 rusts from the holes. On the other hand, when the specific resistance value of the outermost layer is high, the energization points increase, but the resistance per energization point increases, the resistance rollers 10 and / or 11 generate heat, and the ferromagnetic film formed by vapor deposition. This is probably because the gas contained in the metal thin film 2 is generated as outgas, and the adhesion strength between the hard carbon film 3 and the ferromagnetic metal thin film 2 tends to be slightly lowered.
[0041]
As for the specific resistance value of the innermost layer, when the resistance value is increased, it is difficult for the energizing current to flow through the ferromagnetic metal thin film 2 over the entire axial direction of the

resistance rollers

10 and 11. Since it is slightly concentrated, it is considered that recording / reproducing defects tend to increase somewhat, and 0.1 Ω · cm or less is appropriate. Further, the specific resistance value of the innermost layer may be a material that is larger than that of the conductive shaft side surface 23. The closer to the specific resistance value of the conductive shaft side surface 23, the more the conduction resistance from the power source 19 can be suppressed. The outermost layers 10 and 11 are appropriately selected and used according to the balance between the specific resistance value of the outermost layer and the thickness of the resistance material 22.
[0042]
Further, regarding the maximum surface roughness of the outermost layers of the

resistance rollers

10 and 11, the surface shape is transferred to the ferromagnetic metal thin film 2 and / or the non-magnetic insulating base material 1 as it increases, or the

resistance rollers

10 and 11 It is difficult to ensure uniform energization due to any of the energized locations of the outermost layer and the ferromagnetic metal thin film 2 being independent, and recording / reproduction defects tend to increase. This is because the non-magnetic insulating base material 1 provided with the ferromagnetic metal thin film 2 cannot freely move on the surfaces of the

resistance rollers

10 and 11 and the adhesion strength is reduced. It is thought that this is because either the gas component contained in the gas does not escape as outgas from the contact interface between the ferromagnetic metal thin film 2 and the

resistance rollers

10 and 11, Range of .05~1.0μm is appropriate.
[0043]
In any case, because of any of the above reasons, as is clear from (Table 2), sample No. 101 to 118 are sample Nos. Compared to 201-209, both recording and reproduction defects (evaluated by dropout) and corrosion resistance (evaluated by still) are significantly improved. In particular, sample Nos. Formed from the same material from the side of the conductive shaft to the outermost layer of the roller. Compared with 201-204, the improvement effect of evaluation characteristics is remarkable.
[0044]
Although the magnetic recording medium has been described in detail, the present invention can also be applied to the formation of a semiconductor having a conductor and an insulating layer, a printed circuit board, and a liquid crystal conductive film.
[0045]
【The invention's effect】
As described above, according to the present invention, the film quality and uniformity of the thin film formed on the conductive layer provided on the insulating base material can be improved. In particular, when applied to a hard carbon film formed on a ferromagnetic metal thin film of a magnetic recording medium, it eliminates the disadvantage of deteriorating magnetic recording / reproducing characteristics due to minute abnormal discharge and / or energization defects, and provides magnetic recording characteristics and environmental resistance. There is a remarkable effect that it is excellent in reliability and high-speed film formation.
[Brief description of the drawings]
FIG. 1 is a conceptual configuration diagram of an embodiment of an apparatus using a thin film forming method of the present invention.
FIG. 2 is a conceptual cross-sectional view showing the configuration of the magnetic recording medium.
FIG. 3 is a sectional view showing the structure of the resistance roller.
4A is a cross-sectional view illustrating an example of the configuration of a resistive material, and FIG. 4B is a cross-sectional view illustrating another example of the configuration of the resistive material.
[Explanation of symbols]
1 Insulating non-magnetic substrate (Non-magnetic substrate)
2 Ferromagnetic metal thin film
3 Hard carbon film
4 Lubricant layer
5 Backcoat layer
6 Magnetic recording media
7,14 Magnetic recording precursor
8 Magnetic recording precursor
9 Feeding roller
10,11 Resistance roller
12 Main unit (vacuum chamber)
13 Main roller
16 discharge tube
17 Electrode for plasma generation
18 Raw material gas inlet
19 Power supply
20 Vacuum valve
21 Vacuum pump
22 Resistance substances
23 Conductive shaft side
24 Bearing
25 axes
26a-26d resistive material layer
27 Resistance material layer

Claims

The electric resistance value is inclined in the thickness direction around the conductive axis, and the surface of the resistance roller having the surface with the lower electric resistance value as the innermost layer side and the surface with the higher electric resistance value as the outermost layer side. Contacting the outer layer with the ferromagnetic metal thin film;
While applying a voltage to the conductive shaft of the resistance roller, a hydrocarbon reaction gas is supplied to the decompression tank to perform plasma CVD
A method of manufacturing a magnetic recording medium, comprising forming a hard carbon film on a surface of the ferromagnetic metal thin film.

Method for producing a specific resistance of the outermost layer in contact with the ferromagnetic metal thin film of the resistance roller, magnetic recording medium according to claim 1, wherein the range of 1 [Omega · cm or more 500 [Omega · cm.

Resistivity innermost layer of conductive shaft side of the resistance roller, a method of manufacturing the shaft greater than the specific resistance of the side surface, and the magnetic recording medium of claim 1 or less 0.1 [Omega · cm .

The method for manufacturing a magnetic recording medium according to claim 1 , wherein the resistance roller has a maximum surface roughness (Rmax) of 0.05 μm or more and 1 μm or less.

2. The method of manufacturing a magnetic recording medium according to claim 1 , wherein the voltage applied to the conductive axis is at least one selected from a direct current of 0.5 kV to 7 kV and an alternating current of 1 kHz to 5 GHz of the same voltage.

The method of manufacturing a magnetic recording medium according to claim 1 , wherein an inclination of an electric resistance value in the thickness direction of the resistance roller changes stepwise or continuously.

A magnetic recording medium is manufactured by supplying a hydrocarbon reaction gas to a vacuum tank equipped with a resistance roller and forming a hard carbon film on the surface of the ferromagnetic metal thin film formed on the surface of the insulating film by plasma CVD. A device that performs
The resistance roller has an electrical resistance value inclined in the thickness direction, a surface having a low electrical resistance value is an innermost layer side and a surface having a higher electrical resistance value is an outermost layer side,
An apparatus for manufacturing a magnetic recording medium, comprising a conductive shaft for applying a voltage to the shaft of the resistance roller.